<template>
  <div>
    <div>{{ number }}</div>
    <div>{{ numberChange }}</div>
    <input type="number" v-model="number" />
  </div>
</template>

<script>
export default {
  data() {
    return {
      number: 5,
    };
  },
  computed: {
    numberChange() {
      return parseInt(this.number) * 3;
    },
  },
};
</script>